Nothing is exact - enables you to make educated decisions
10/90 rule - spend 10% of budget on tool and 90% on people who use the tool. (use the free solution like Google. We need to get way better at using it)
sitescan or wasp will tell you if analytics is on your page - and working
What do you do with this data overload?
Filters - like an all lowercase filter, www and no wwww - cleans up your analytic data